Two main types of the energy device are an energy storage device and an energy generating device. Typical examples of the energy storage device are an electrochemical capacitor and a battery, which have already been used in their appropriate markets. Examples of the electrochemical capacitor are: an electric double layer capacitor which uses an activated carbon as a polarizable electrode and utilizes only an electric double layer formed at an interface between a pore surface of the activated carbon and an electrolytic solution; and a redox capacitor which uses a transition metal oxide, such as ruthenium nitrate, whose valence continuously changes, and an electrically-conductive polymer which can be doped. Moreover, two main types of the battery are: a secondary battery which can be charged and discharge by utilizing intercalation and chemical reactions of active materials; and a primary battery which is basically not rechargeable after being discharged once.
The most basic component common to all of these various energy storage devices is an electrode active material which can discharge energy in principle. In addition, to take out the energy stored in the electrode active material, a current collector (electric conductor) is further required, which has electron conductivity and is electrically connected to the electrode active material. Since the current collector needs to transfer the energy of the electrode active material with high efficiency, a metallic material, such as aluminum, copper, or stainless steel, which is very low in resistance is typically used as the current collector. However, in the case of using the electrolytic solution, such as a sulfuric acid aqueous solution, which causes metal to corrode, for example, a rubber-based material to which electrical conductivity is given may be used as the current collector.
As the application of the energy storage device is increasing in recent years, there is a need for the energy storage device which has excellent properties, i.e., which is lower in resistance and can discharge higher current. First, these properties were expected of the electric double layer capacitor which was the lowest in resistance in principle among the energy storage devices, and the electric double layer capacitor having such properties were realized by disposing a carbon-based electrically-conductive layer on a joint surface between the electrode active material and the current collector. Since an electronic resistance in the electrode active material of the electric double layer capacitor is comparatively lower than those of the other secondary batteries, a contact resistance between the electrode active material and the current collector accounts for a nonnegligible percentage with respect to the resistance of a device, so that the carbon-based electrically-conductive layer is disposed on the joint surface. At present, similar technical trend to the above has been pursued for a lithium secondary battery.
To solve the above problems, an energy device has been studied which uses as the electrode active material a carbon nanotube whose one end is connected to the current collector (see Patent Document 1 for example). The carbon nanotube is a hollow carbon material having a minimum diameter of 0.4 nm and a maximum length of 4 mm. Unlike conventional pellet electrodes, a carbon nanotube electrode in which one end of the carbon nanotube is connected to a substrate does not require an electric conduction assisting material and a binding material. Therefore, a volume fraction of the active material is 100%. In addition, since the carbon nanotube is connected to the current collector that is the substrate, the carbon nanotube electrode is very low in electrical resistance. Further, the carbon nanotube has an extremely high ideal specific surface area of 2,625 m2/g, and is especially suitable to be applied to the electric double layer condenser.
However, in the case of forming the energy device having a rolled structure using the current collector having flexibility, the problem arises where a carbon nanotube layer floats or peels. Therefore, it has been extremely difficult to apply the carbon nanotube electrode to the energy device having the above structure.
Patent Document 2 discloses that in the rolled-structure lithium secondary battery, a slit is formed in an active material non-coated region located along a long side of the substrate itself. This prevents wavy distortion and wrinkles of the substrate, which are generated by pressure applied by a roll press because of the difference in thickness between an active material coated region and the active material non-coated region. Patent Document 2 does not describe that the carbon nanotube is used as the active material, and the non-coated region is formed to extend in a direction parallel to a short side of the substrate. Moreover, Patent Document 2 does not describe the problem of peeling of the substrate and the active material due to rolling.
Patent Document 3 discloses that in an electrode for use in a lithium secondary battery in which a thin film of a metal alloyed with lithium is formed on the substrate, voids of a predetermined pattern are selectively formed on the thin film. This is to absorb volume expansion caused by the intercalation of the lithium ion at the time of charging. Moreover, Patent Document 3 does not describe that the carbon nanotube is used as the active material, and does not describe the problem of peeling of the substrate and the active material due to rolling.
Patent Document 4 describes that in the electric double layer capacitor including the polarizable electrode formed by the carbon nanotube formed on an electrode forming region of the substrate, the carbon nanotube is formed in the electrode forming region except for a predetermined region. This aims to obtain large electric capacity from initial charging and discharging and obtain large electric capacity even at low temperature, by facilitating impregnation of an inside of the carbon nanotube with the electrolytic solution. Moreover, Patent Document 4 does not describe the rolling of the substrate and the problem of peeling of the substrate and the active material due to the rolling.    Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2005-353758    Patent Document 2: Japanese Laid-Open Patent Application Publication No. 2000-208129    Patent Document 3: Japanese Laid-Open Patent Application Publication No. 2004-127561    Patent Document 4: Japanese Laid-Open Patent Application Publication No. 2005-259760